Adhesive compositions

ABSTRACT

Disclosed are blends of polyesters and esters of glycerin or propylene glycol which are useful as hot-melt adhesives for fabrics.

DESCRIPTION

1. Technical Field

This invention relates to blends of polyesters and esters of glycerin orpropylene glycol which are useful as hot-melt adhesives for fabrics.

2. Background of the Invention

Certain low-melting polyesters in powder form are useful as fabricadhesives. One method of using the powder involves the making of fusibleinterlinings which are subsequently bonded to a face fabric. Forexample, fusible interlinings are used in the manufacture of suits, inshirt collars and cuffs, and in the waistband of trousers. Powders arealso useful as binders in nonwoven fabrics. Powders used in theseapplications are generally coarse (40-70 mesh or 0.42-0.21 mm), medium(70-200 mesh or 0.21-0.07 mm), or fine powders (<200 mesh or <0.07 mm).

In commercial bonding applications such as the bonding of a fusibleinterlining to a face fabric, the faster the powder melts and flows outto make a bond the more economical the process becomes. Increasing themelting rate of the powder increases line speed and production rate andreduces the exposure time of the fabric to intense heat.

Various polymeric powders are used in these processes includingpolyesters, polyethylenes, polyamides, poly(vinyl chloride), and thelike. Polyesters are a major type of adhesive used in theseapplications.

A need has existed for an additive that could substantially increase themelt down rate of polyester powders without adversely affecting bondstrength. Such an adhesive would provide an economic advantage in fasterline speed and increased production rates with the same equipment.

It has now been found that low melting compounds such as acyl esters ofpropylene glycol and glycerin having melting points of about 35° toabout 75° C. significantly increase the melt down rate of the polyesterpowders compared to the melting rate of the unmodified powders.

DISCLOSURE OF THE INVENTION

According to the present invention, adhesive compositions are providedwhich are described as polyester hot-melt adhesives containing about 0.2wt. % to about 25 wt. % of low-melting esters of propylene glycol orglycerin which have melting points of about 35° to about 75° C. Thesecompositions, which show increased melting rates over the unmodifiedpolyester and allow the use of lower bonding temperatures, are useful asfabric adhesives.

The adhesive compositions comprise

(a) a polyester derived from 100 mole % of an acid component comprisingterephthalic acid, isophthalic acid, a mixture of terephthalic andisophthalic acid or hexahydroterephthalic acid and a glycol componentcomprising at least one glycol having from 2 to 12 carbon atoms, thepolyester having a melting point of about 80°-180° C. and a heat offusion of less than 10 calories per gram, and

(b) from about 0.2% to about 25% based on the weight of the polyester ofa compound selected from ##STR1## wherein R₁ is ##STR2## or H and R₂ andR₃ are each ##STR3## or H, and at least one of R₁, R₂ and R₃ is ##STR4##

It should be understood that the rest of the valences in the above acylgroups are satisfied with hydrogen.

The acid component of the polyester comprises at least 50 mole % of atleast one of the following acids: terephthalic acid, isophthalic acid, amixture of terephthalic and isophthalic, and hexahydroterephthalic acid(sometimes called 1,4-cyclohexanedicarboxylic acid). Up to 50 mole % ofthe acid component may be an aliphatic or cycloaliphatic dibasic acidcontaining 4 to 12 carbon atoms other than hexahydroterephthalic acid.Preferred acid components comprise at least 60 mole % terephthalic acid.Other preferred acid components comprise at least 60 mole % terephthalicacid with up to 40 mole % being isophthalic or glutaric acid.

The glycol component of the polyester comprises at least one glycolhaving from 2 to 12 carbon atoms. Preferred glycol components compriseat least one of the following glycols: ethylene glycol, diethyleneglycol, 1,4-butanediol and 1,6-hexanediol. Other preferred glycolcomponents contain at least 80 mole % of a mixture of 1,4-butanediol and1,6-hexanediol, and at least 80 mole % of a mixture of diethylene glycoland 1,4-butanediol.

The polyesters useful in the practice of this invention are thosecrystalline or semi-crystalline polyesters having melting points ofabout 80° to about 180° C. with heats of fusion of less than 10 caloriesper gram. Preferred polyesters have melting points of about 100° C. toabout 150° C. The inherent viscosity of these polyesters may range fromabout 0.4 to about 1.2 but the preferred range is about 0.5 to about1.0. Many such polyesters are commercially available, and they may beproduced by conventional methods well known in the art.

An additive that substantially increases the melt down rate of polyesterpowders without adversely affecting bond strength obviously provides aneconomic advantage in faster line speeds and increased production rateswith the same equipment. It is important that the additive notdeleteriously affect the good free flowing characteristics of thepolyester powders.

It has now been found that low melting compounds such as saturated acylesters of propylene glycol and glycerin having melting points of about35° to about 75° C. significantly increase the melt down rate of thepolyester powders compared to the melting rate of the unmodifiedpowders.

These additives may be added to the polyesters by melt blending afterwhich the polymer blend is ground to the desired particle size, bycogrinding the polyester with the additive, or by making blends ofcoarse, medium, or fine powders of each component.

The low melting additives useful in the practice of this invention areacyl esters of propylene glycol and glycerin with at least one acylgroup containing 14 to 20 carbon atoms. These esters may also containone or more acyl groups containing 2 to 6 carbon atoms ##STR5##(succinic acid radical). The concentration of low melting additive mayrange from about 0.2 wt. % to about 25 wt. % but the preferredconcentration range is about 1 to about 20%.

Some suitable additives which are available commercially are theMyvaplex® glyceryl monostearate, Myverol® distilled monoglycerides,Myverol distilled propylene glycol monoesters, and Myvacet® distilledacetylated monoglycerides supplied by Eastman Chemical Products,Incorporated.

These mono-, di- or tri-esters of glycerin and propylene glycol may beproduced by conventional methods well known in the art.

Polyester powder blends containing the low melting additives arefree-flowing powders which may be readily applied to fabrics byconventional random sprinkling, powder point, or paste applicationmethods. These powder blends may also be applied from electrostaticspray guns. It was also found that the presence of the additivesubstantially decreases the bonding temperature of the polyesteradhesive. This fact is especially important when temperature sensitivefabrics are used, when faster fabric assembly rates are desired or whenold presses with limited temperature capabilities are used.

The following examples are submitted for a better understanding of theinvention.

EXAMPLE 1

One hundred grams of a polyester consisting of 80 mole % terephthalicacid, 20 mole % isophthalic acid, 80 mole % 1,6-hexanediol, and 20 mole% 1,4-butanediol and having an inherent viscosity of 0.72 (in 60/40phenol/tetrachloroethane solution at 23° C.), a melting point of 104°C., and a glass transition temperature of 12° C. is cryogenically groundin liquid nitrogen in a Mikro Pulverizer using a 2 mm screen. The powderis dried at 60° C. under vacuum overnight and screened with agitationfor 15 minutes to provide coarse powder, medium powder, and fine powder.

Approximately 0.01 g of the medium powder is placed in a symmetricalpile on a glass slide. The slide containing the powder is placed on ahot plate surface maintained at 155° C. The polyester powder has a meltdown time (time for the powder to completely melt) of 16.6 seconds.

EXAMPLE 2

The polyester described in Example 1 (55.25 g) and 9.75 g of a distilledmonoglyceride derived essentially from glycerin and stearic acid andhaving a melting point of 69° C. and designated commercially as Myverol18-06 (Eastman Chemical Products, Inc.) are blended in a BrabenderPlastograph mixer at 135° C. for five minutes in the melt phase undernitrogen. The polyester/monoglyceride blend is cryogenically ground inliquid nitrogen in a Mikro Pulverizer using a 2 mm screen. The powder isdried overnight at 60° C. under vacuum and screened with agitation for15 minutes to provide coarse powder, medium powder, and fine powder.

Approximately 0.01 g of the medium powder is placed in a symmetricalpile on a glass slide. The slide containing the powder is placed on ahot plate surface maintained at 155° C. The polyester powder has a meltdown time of eight seconds.

EXAMPLE 3

The procedure of Example 1 is followed except that the polyesterconsists of 70 mole % terephthalic acid, 30 mole % glutaric acid, 45mole % diethylene glycol, and 55 mole % 1,4-butanediol. The polymer hasan inherent viscosity of 0.83 (in 60/40 phenol/tetrachloroethane),melting point of 109° C., and a glass transition temperature of 6° C.The melt down time of this polyester is 14.6 seconds.

EXAMPLE 4

The procedure of Example 2 is followed using the polyester described inExample 3 with the following concentrations of Myverol 18-06monoglyceride. The melt down times of medium powder of thesecompositions are given below with the compositions.

    ______________________________________                                                   Myverol 18-06                                                      Polyester  Monoglyceride                                                                             Melt Down Time                                         g          g           sec                                                    ______________________________________                                        63.7       1.3     (2%)    12.6                                               61.75      3.25    (5%)    8.0                                                58.50      6.5     (10%)   8.1                                                55.25      9.75    (15%)   7.9                                                ______________________________________                                    

Similarly good results are obtained with powder blends.

The medium powder containing 5 wt. % Myverol 18-06 is coated on cottoninterlining fabric using a wheel applicator (coating conditions were:heated roll 180° C.; chill roll 13° C.; line speed 3-3.7 meters/minute,fusion temperature variac setting 60-75%) to provide fusible interlininghaving a coating weight of 22.9 g/m² (19 g/yard²). The coatedinterlining is bonded to 65:35 polyester:cotton fabric using anelectrically heated press. The unmodified medium powder is applied in alike manner for a control.

The unmodified powder requires a minimum bonding temperature of 120° C.and a 15 second dwell time to give a T-peel bond strength of 0.215 kg/cm(1.2 pli), compared to a minimum bonding temperature of 100° C. and 15seconds dwell time for the composition containing 5% Myverol 18-06 togive a bond strength of 0.1786 kg/cm (1.0 pli).

EXAMPLE 5

The procedure of Example 1 is followed except that the polyesterconsists of 100 mole % terephthalic acid, 80 mole % 1,6-hexanediol, and20 mole % 1,4-butanediol. The polymer has an inherent viscosity(determined in 60/40 phenol/tetrachloroethane solution) of 0.72, meltingpoint of 125° C. and a glass transition temperature of 12° C. The meltdown time of this polyester is 24.9 seconds.

EXAMPLE 6

The procedure of Example 2 is followed to blend the polyester describedin Example 5 with 10 wt. % of a propylene glycol monoester commerciallyavailable as Myverol P-06. The melt down time of medium powder of thisblend is 12.1 seconds.

Similarly good results are obtained using Myvaplex 600 glycerylmonostearate; Myvacet 7-07; or Myvacet 5-07) acetylated monoglyceridesor Myverol 18-06 monoglyceride.

In all the above examples according to this invention, the ΔH_(f) of thepolyester is less than 10 cal/gm.

Whenever the term "inherent viscosity" (I.V.) is used in thisapplication, it will be understood to refer to viscosity determinationsmade at 25° C. using 0.50 gram of polymer per 100 ml. of a solventcomposed of 60 wt. % phenol and 40 wt. % tetrachloroethane.

The "melting point" (T_(m)) of the polymers described in thisapplication are readily obtained with a Differential ScanningCalorimeter.

The "heat of fusion" ΔH_(f) of polymers is the amount of heat absorbedwhen crystallizable polymers are melted. ΔH_(f) values are readilyobtained using Differential Scanning Calorimeters (Perkin-Elmer). Forexample, one method for determining ΔH_(f) is described in Journal ofApplied Polymer Science 20, 1209 (1976). Measurement of ΔH_(f) is alsodescribed in duPont Thermal analysis Bulletin No. 900-8 (1965).Qualitatively it is possible to compare the degree of crystallinity ofpolymers by comparing their ΔH_(f) values.

The strength of the bonds is determined by the so-called "Peel Test"based on a modification (i.e., three test specimens) of the ASTM "T-PeelTest" set forth on pages 63 and 64 of the 1964 edition of the BOOK OFASTM STANDARDS, published by the American Society for Testing Materials,and more specifically identified as Test Number D-1876-61-T.

Unless otherwise specified, all parts, percentages, ratios, etc., are byweight.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

We claim:
 1. Adhesive composition comprising(a) a polyester derived from 50 to 100 mole % of an acid component comprising terephthalic acid, isophthalic acid, or a mixture of terephthalic and isophthalic acid, and a glycol component comprising at least one glycol having from 2 to 12 carbon atoms, said polyester having a melting point of about 80°-180° C. and a heat of fusion of less than 10 calories per gram, and (b) from about 0.2% to about 25% based on the weight of said polyester of an ester selected from ##STR6## wherein R₁ is ##STR7## or H and R₂ and R₃ are each ##STR8## or H, and at least one of R₁, R₂ and R₃ is ##STR9##
 2. Adhesive composition according to claim 1 wherein said polyester comprises at least 60 mole % terephthalic acid.
 3. Adhesive composition according to claim 2 wherein said polyester comprises up to 40 mole % isophthalic or glutaric acid.
 4. Adhesive composition according to claim 1 wherein said glycol component comprises at least one glycol selected from ethylene glycol, diethylene glycol, 1,4-butanediol and 1,6-hexanediol.
 5. Adhesive composition according to claim 1 wherein said ester is at least 60% by weight of a monoester of glycerin.
 6. Adhesive composition according to claim 1 wherein said ester comprises an ester of propylene glycol.
 7. Adhesive composition according to claim 1 wherein said ester comprises an acetylated monoglyceride.
 8. Adhesive composition according to claim 1 wherein said ester comprises a succinylated monoglyceride. 